Eyepiece-prism



' F. E. WRIGHT.

EYEPIECE PRISM.

APPLICATION men JUNEZG, I919.

1,370,938, Patented Mar. 8, 1921.

2 SHEETS-SHEEI I.

UNITED STATES FRED ERICK E. WRIGHT, OF WASHINGTON, DISTRICT OF COLUMBIA.

EYEPIEGE-IPRISM.

Specification of Letters Patent.

Patented Mar. 8, 1921.

Application filed June 26, 1919. Serial No. 307,011.

(FILED UNDER. THE ACT OF MARCH 3, 1883, 22 STAT. I..,.625.)v

To all whom z'tmay concern Be itknown that I, FREDERICK E. lVRIoHT, acitizen of'the United States, and a resident. of Washington, D. 0., have invented an Improvement in Eyepiece Prisms, of which. the following is a specification.

The invention described herein may be used by the Government, or any of its officers or employees in prosecution of work forthe Government, or by any other person in the United States, without payment of any royalty thereon.

Iy invention relates to new and useful improvements in the arrangement and type of eye piece prisms used in base line telemeters.

The objects are simplicity of construction, freedom from cemented and also from silvered surfaces, both of which are liable to give trouble in the course of time, the former because of decrease in transparency and of strains and slight shifts which may be in troduced by the drying out of the cement, and the latter by the deterioration of the silveredv surfaces.

Figure 1' is: a top. view. of my invention giving an erect image.

Fig. 2 is a side view of the same.

Fig. 3 shows the image in the field of view as seen by the observer.

Fig. 4 is a plan view of an arrangement of risms which produces an inverted image.

ig. 5 is an elevation of same.

Fig. 6 shows the image in the field of view as seen by an observer.

Figs. 7 and 8 show plan and elevation of eye piece prisms in which the emergent rays are inclined at an angle of thirty degrees to the vertical.

Figs. 9 and 10 show a similar arrangement for an inverted image.

Figs. 11 and 12 show prism arrangements for rays emer ing at forty-five degrees to the vertical. ig. 11 gives an erect image while prism 2 of Fig. 12 gives an inverted image.

Fig. 13 is an end view, showing a rhomb shaped prism attached to the upper prism.

Instruments of the type to which this invention is applicable consist usually of a pentagonal prism at each end of a base line of fixed length, which prisms reflect the light rays from the object whose range is being measured, into the tube which houses separate optical systems in each half, consisting principally of the penta prisms above mentioned, the objective lenses, the an 1e measuring prism, and the coincident or eviating prisms which reflect the light from each end of the telescopeinto theeye piece.

This invention relates particularly to the type ofdeviating prisms used for the purpose of securing'the coincidence of the images. The eye piece prism consists of two prisms 1 and 2, the prism 1 in this case being superimposed upon. the prism 2 so that their hypotenuse surfaces 3 and 4- cross as indicated in Fig. 1. The range finders field of View is divided into two partsv by the horizontal line 5, in Fig. 3,. formed by the edge 6 of. the total reflecting prism surface 7 Figs. 4 and 5 are prisms of different shape similarly disposed as in Fig. 1 but the lower prism 2 giving three reflections and. therefore an inverted image as shown at thetop of Fig. 6.

The reflecting surfaces of prism- 2, Fig; 2, are of the roof-edge type, including an angle of ninety degrees Wlth each other and. their line of intersection including an angle of forty-five degreeswith the side surfaces of the prism.

Figs. 7 and 8-show a disposition; of prisms. similar to Fig. 1, except that the last reflecting surfaces 7 and 8 are at such an angle that the emergent rays are inclined at an angle of thirty degrees to the vertical.

Figs. 9 and 10 are similar to Figs. 7 and 8 except that the reflecting surfaces of prism 2 are shaped so as to give three reflections and, therefore, an inverted image.

Figs. 11 and 12 show views of prism arrangements for rays emerging at forty-five degrees to the vertical, Fig. 11 giving an erect image'while the prism 2 of Fig. 12 gives an inverted image.

In case it is desired to have the rays from both objectives pass along the axis of the tube, a small rhomb shaped prism 3 is used as in Fig. 13 to raise the line of sight, from the optical system of one side, so that the upper prism will function properly.

The rhomb shaped prism may be secured to the upper prism by cementing it to one of its side surfaces or by placing the two prisms in optical contact. The second method requires a high degree of skill in manufacture but the finished prism has then an advantage of remaining fixed in position and free from strains and slight shifts which may be introduced by the drying out of the cement.

It will be understood that the angle of incidence in each of the cases cited above is greater than the critical angle of the glass thereby giving total reflection and doing awa with the necessity of silveredsurfaces.

T e path of rays of light passing through the prisms of Fig.1 isas indicated by the rays R and 1'. The rays R coming from the right hand'end of the tube are reflected by surface 3'to surface 7 and thence into the ocular, being reflected perpendicular to the exit surface 9. The rays 7 coming from the left hand end of the tube are reflected by surface 4 to surface 8 and thence into the ocular being reflected perpendicular to the exit surface 10. The images thus formed are brought into coincidence as shown in In Figs. 4 and 5, the rays R are reflected at R and R as described under Fig. 1 while the rays 1' entering the lower prism are reflected by the roof-edge surfaces 11 and 12 to the surface 8 as indicated by r, r and thence into the ocular, the emergent rays i being pei pendicular to the exit surface 10.

rom'the description'of the reflections in Figs. 1 to 6, it is believed the operation of the modifications shown in the remaining figures will be clear.

In Figs. 7, 8, 9, 10, 11 and 12, the reflecting surfaces are so arranged that the emergent rays make an angle with the vertical which is less than a right angle.

In Fig. 13 the rhomb shaped prism 3 is attached to the upper rism 1 in order to raise the line of sight 0 the right hand optical system so that the rays will pass through the upper prism and be reflected as described above.

The separate optical system in each half of the tube or telescope body, transmits light to a common field eyepiece, so that the partial images of the target may be seen simultaneously. The modifications shown in the comprising a plurality of total reflecting surfaces for reflecting the light rays from each optical system into the ocular, the edge of one of the total reflecting surfaces formin of view, the last'reflecting surface of each prism being so disposed as to give the emergent rays a predetermined angle with relation to the plane of the measuring triangle.

2. In a base line telemeter in which the light rays from both objectives are along the axis of the tube, two deviating prisms, one superimposed upon the other, a rhomb shaped prism for reflecting the rays from one of the objectives to the deviating prism which is not in alinement, the two last men tioned prisms being placed in optical contact.

FREDERICK E. WRIGHT.

a horizontal dividing line in the field 

